Abstract

Neurophysiological research has established that a transient stimulus, spatially located outside the receptive field of visual cells, can activate some cells and inhibit firing in others. However, the significance of this phenomenon for behavioural responses in man is unclear. This study investigated the effect of a transient peripheral event on the initiation of saccadic eye movements to a luminance increment. In Experiment 1 human saccadic eye movements to targets that varied in luminance were compared on 'shift' trials, in which the saccadic target was timed to coincide with a step displacement of a vertical grating in the background, and on 'no-shift' trials, when the background remained stationary. The results showed a significant delay in mean saccadic latencies on 'shift trials' compared to 'no-shift' trials. Saccadic latencies were reduced in both conditions with increasing target intensity. Measurement of visual sensitivity showed a small non-significant increase in thresholds in the background 'shift' condition. A second experiment manipulated visuo-temporal information by varying both target duration and intensity. This experiment revealed significant effects of target duration and signal intensity on saccadic latency; and a 3-way interaction showing that saccades suffered the greatest delay in the background 'shift' condition at the lowest duration and intensity targets. These results show that the peripheral motion of visual texture delays the programming of saccadic eye movements and there is a particularly marked effect for targets of low signal strength.